It's never a bad idea to be prepared for emergencies, and a pantry full of canned foods is one way to cope with power outages and other inconveniences. Cans don't require electricity, with fridge or freezer space, and even the strongest winds and rain pose little short-term threat to their safety. Canned vegetables won't last forever, but their usable life goes well beyond any date stamped on the can.

Expiration Date vs. Use-By Date

The dates on consumer food products have different meanings, and it's important to understand the difference. An expiration date indicates that a food is no longer safe once the date has passed. Among common canned foods, only infant formula has a hard-and-fast expiration date. It's more common to see a use-by date, which provides a conservative guide to the food's limitations in flavor and quality. Manufacturers set their own use-by dates, and these dates are unrelated to the product's safety. In many cases, the can contains only a production date, and you'll have to work out the shelf life for yourself.

Shelf-Life Math

Canned goods are highly durable, so the limits of your shelf life are flexible. High-acid vegetables and vegetable products such as tomatoes, tomato sauce and sauerkraut usually recommend no more than 12 to 18 months' storage. That's because they can slowly erode the cans' non-reactive lining, eventually discoloring or developing off flavors. Most other vegetables, with their relatively low levels of acid, are safe for two to four years. If the cans aren't stamped with a date, label them yourself with a felt marker or a stick-on label so that you can monitor them and eat the oldest first.

Limitations and Danger Signs

Cans store best in a dry environment, at temperatures below 75 degrees Fahrenheit. If they're routinely subjected to higher temperatures, their quality will degrade more quickly. Cans that freeze should be discarded. Rusted cans can still be safe, if the rust is confined to the surface, but cans pitted with rust might not be airtight any longer. They should be discarded. So should swollen cans, or cans with a dent on the seam or a deep, sharp dent. Leaky cans should also be discarded. If a can sprays when you open it, or the contents appear to be under pressure, it's likely unsafe and should be discarded.

Once the Can Is Open

Those shelf-life guidelines apply only to unopened cans. Once you've opened your vegetables, they're as perishable as any other prepared food. Any unused or leftover canned vegetables should be refrigerated within two hours, to keep them food safe. Like other leftovers, they're best and safest if used within 3 to 4 days of being opened. If you're unlikely to eat the remaining vegetables before that time, you can bag and freeze them for later consumption.

About the Author

Fred Decker is a trained chef and certified food-safety trainer who has written and blogged on food-related topics since 2007. Previously he sold computers, insurance and mutual funds. He is a former columnist for the Saint John, New Brunswick "Telegraph-Journal," and has been published in Canada's "Hospitality and Foodservice" magazine as well as online on many high-profile websites. Decker was educated at Memorial University of Newfoundland and the Northern Alberta Institute of Technology.